Responsiveness to γ-chain cytokines by different NK-cell subsets. (A) Ex vivo staining of CD25 (IL2Rα chain), IL15Rα chain, CD122 (IL15/IL2Rβ chain), and CD132 (common γ chain; open histograms) and corresponding isotype control staining (gray-filled histograms) on CD56^bright, CD56^dim CD62L⁺, and CD56^dim CD62L⁻ NK cells. Percentages of positive cells and median fluorescence intensity (MFI) values of specific staining minus MFI of isotype staining of 1 representative donor of 3 are depicted. (B-D) Levels of p-STAT5 after stimulation of sorted NK-cell subsets with 100 ng/mL IL-15 or 100 ng/mL IL-2 for 15 minutes. (B) One representative experiment of 6 for IL-15 and of 4 for IL-2 is shown. Stimulated cells (open histograms) and unstimulated controls (gray-filled histograms) are depicted. MFI values of stimulated minus MFI of unstimulated controls and frequencies of p-STAT5⁺ cells are shown in each plot. (C) Mean value of p-STAT5 MFI ± SEM after IL-15 stimulation of 6 independent experiments is shown. *P < .05 as calculated by Wilcoxon test. (D) Western blot analysis of p-STAT5^T694 levels after stimulation of sorted NK-cell subsets with or without 100 ng/mL IL-15 for 15 minutes (top panel) and ex vivo levels of total STAT5a and STAT5b (bottom panel) are shown. One representative experiment of 4 is shown. Numbers under the β-actin bands represent signal intensity displayed by each band normalized to β-actin (mean value ± SEM of 4 independent experiments).